when use DPM to calculte the coupled solid-gas two-phase flow, mass flow rate should be predetermined, so the number of particles injected per time step could be calculated(if particles have the same density and size):

every time step, "num" particles would be injected from one particle stream, on the console window, it would be told one particle has been injected(let's call it mother particle), that is to say "num" son particles are included in one of this kind of mother particles.

my problem is ,when i caught every mother particles injected, through recording the particles impacted the wall, i found the number of son particles in it is not the same as "num", and even different from one to another, would you please tell me how to determine the number of particles included in every mother particles injected? thanks in advance!

Maybe this has to do with what happens during the way to the wall? Are you using any breakup models, for example? Try checking closer to the injection?

Otherwise, you're right; Fluent injects one parcel per timestep, which represents a number of real particles that should be easily determined from the parcel mass and the individual particle mass, where the parcel mass is given by mass flow rate and time step size of the injection.